Former Italy striker Luca Toni hit a brace for Fiorentina as La Viola compounded Siena's Serie A struggles with a 4-1 win that moved them up to fifth on Sunday.
Toni, who saw strike partner Stevan Jovetic play an hour on his return from injury, headed Fiorentina's opening goal in the 16th minute.
Chilean David Pizarro doubled the hosts' lead from the penalty spot minutes later and it was 3-0 at the interval after Alberto Aquilani tapped home an easy shot on the stroke of half-time.
Siena are rooted to the bottom of the table and they never looked a threat against Vincenzo Montella's side.
Brazilian striker Reginaldo came off the bench on the hour mark and 10 minutes later ran on to a through ball to beat compatriot Noberto Neto in the Fiorentina goal with a well-struck shot.
However Toni made sure Fiorentina had the last word, the big striker heading home past Gianluca Pegolo in the 79th minute to help the hosts leapfrog Roma into fifth place.
Siena finished with 10 men when defender Massimo Paci was shown a second yellow card in the dying minutes.
Serie A leaders Juventus hold a four-point lead over Inter Milan but can extend that to seven points with a win over Atalanta later Sunday.